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A chimney has
two important functions. It brings fresh air to the fire in the
fireplace and it provides an escape for smoke and harmful gases.
There is a
temperature difference in the cold air outside the chimney and the
heated air in the chimney, so an upward flow is created--a suction
that is called the “draft.”
The flue is a
long channel in the chimney through which smoke and combustion gases
are conveyed to the outside. Flues are usually lined in order to be
efficient and safe. Certain materials are specified for the lining by
local building codes. Usually a flue is lined with terra cotta tile,
or round, glazed tile.
The extension
of the fireplace is called the hearth. The hearth protects the area
immediately around the fireplace from damage from sparks or hot ashes.
A hearth is constructed at or above floor level of noncombustible
material like brick, stone, marble or a combination of these
materials.
The space
formed by the back and sides of the fireplace is called the firebox.
This is where you actually build the fire. The walls of the firebox
are constructed of solid masonry or reinforced concrete and are
usually, per building codes, no less than eight inches thick. These
walls are then lined with two-to-four inches of firebrick that's set
with a heat-resistant mortar called fireclay. Steel lining at least a
quarter-inch thick can also be used. Firebrick not only protects the
structure but because of its refractory qualities, retains heat and
then throws it back into the room.
At the top of
the firebox there is a hinged damper, a sort of lid that fits into the
throat of the fireplace. The damper's main purpose is to insure all
smoke from the fire gets pulled into the flue and then up and out of
the house. The damper also prevents warm air in the house from
escaping up the chimney when there is no fire in the fireplace.
Debris, rain and the occasional bird are also kept from falling into
the fireplace. The damper should always be closed when the fireplace
is not in use and opened, of course, first thing when you're getting
ready to build a fire.
The smoke
shelf lies directly behind the damper, and provides the foundation for
the smoke chamber which is the space between the smoke shelf and the
flue. The smoke chamber is where smoke and gases collect and wait to
exit up the flue. Smoke doesn't fly up the chimney all at once. It's
funneled up a pathway that begins within the smoke chamber.
Once the flue
gets hot and a good draft is established, it continuously sucks the
air, smoke and gases out of the fire and exhausts them out through the
chimney. If this isn't happening when you build a fire and smoke pours
into the room rather than up and out the chimney, you'll need to
assess the draft situation. Start by making sure the damper is fully
opened. If the damper is open and the smoke isn't going up the
chimney, extinguish the fire. When everything is cold, launch an
investigation to uncover the problem.
Protect
your eyes with goggles and cover your hair. Open the damper and shine
a flashlight into the smoke chamber. Look for blockages like leaves,
sticks and anything else that looks like a nest. If your chimney isn't
capped, birds, raccoons and squirrels might build a nest in this
wonderful, secure place. If you discover shards of tile or brick, they
are a sign of a deteriorating chimney which will require the attention
of an expert. If you note blockages of any kind, discontinue the use
of the fireplace until you've been given the go ahead by the expert.
A chimney cap
costs anywhere from $60 to $1000 and can save you much more by
blocking rainwater that will eventually erode bricks and mortar. A
chimney cap usually contains a metal spark arrester that breaks up
sparks before they can drift to your roof or the neighbors' trees. A
cap on the chimney will keep animals from setting up housekeeping
inside the chimney.
Creosote is
another problem for chimneys. Every fire deposits creosote inside the
chimney and eventually the deposits harden. It can block the flue and
dissolve mortar and it's highly flammable. Creosote ignites in a
chimney with a roar similar to a freight train, sending fireballs into
the room and out onto the roof. This type of fire burns so furiously,
it's nearly impossible to contain. The intense heat can heat the wood
in the house beyond the chimney and burn the house to the ground in no
time.
You can find
a chimney sweep in the Yellow Pages. Choose one that has been tested
and certified by the Chimney Safety Institute of American (CSIA).
Chimney sweeps are trained not only in the ways to clean a chimney but
also in the area of repair, building codes, installation and the
formulation of drafts. The sweep will clean the chimney and assess it
for safety, point out any signs of deterioration and recommend
repairs. An annual inspection is vital to the safe enjoyment of your
fireplace.
Copyright 2004
PropertySource Network |
